1. Field of the Invention
The present invention relates to a high-frequency heat -sealing apparatus f or use in a filling/packing machine f or producing liquid beverages or the like which are packed in paper containers so that they can be stored for a long time, and more particularly, to a high-frequency heat-sealing apparatus for transversely high-frequency heat-sealing a tubular packing material filled with contents such as liquid beverages, together with a fluid, by using a sealing jaw and an opposing jaw which do not have a ridge on their action faces.
2. Description of the Related Art
Hitherto, when a packing container having a box shape or the like filled with a liquid such as juice in a sealed manner is to be produced, as seen in Japanese Patent Publication No. 3215/1980, it is well known to use a sealing apparatus in which a packing material of a laminate of paper, an aluminum foil and a synthetic resin is used and continuously formed into a tubular shape while being conveyed. The tubular packing material is transversely heat-sealed with a fluid by using pressing means including a sealing jaw having a high-frequency coil and an opposing jaw having a sealing rubber of a hard rubber, and is cut between two sealed zones having been heat-sealed by a cutting blade.
Moreover, in Japanese Patent Laid-Open Nos. 134744/1983, 269854/1993, 164523/1995 and 240607/1997, there are other disclosures of a heat-sealing apparatus for heat-sealing a laminate material in which a ridge having a rectangular shape in the cross section is formed on the action face of a high-frequency coil on a sealing jaw in the aforementioned heat-sealing apparatus so that the molten resin is extruded into a sealed zone by the ridge. In order to avoid a problem of the aforementioned heat-sealing apparatus that when the molten resin is guided to flow toward the container's interior side of the sealed portion of a tubular packing material, corrugated molten resin beads are formed on the edge portion of the container's interior side so that cracks start from the crests of the beads to break the container when an external force is applied to the container, two magnetic members are arranged on the outer side (or on the container's interior side) of the straight portions of a U-shaped high-frequency coil to leave the portion of the container inner side unheated, as disclosed in Japanese Patent No. 2,571,977.
Furthermore, in Japanese Patent Laid-Open No. 230834/1996, it is described that in the aforementioned heat-sealing apparatus, a high-frequency coil, which has a ridge in its longitudinal direction and grooves formed on the two sides of and in parallel with the ridge, causes molten resin to remain in the grooves without flowing out of a sealed zone, even if the resin on the packing material is melted and pushed by the ridge. In Japanese Patent Laid-Open No. 244728/1996, it is described that in the aforementioned heat-sealing apparatus, there is the use of a high-frequency coil which is inclined gradually at the more distance as the sealed zone forming portion goes to the outer side (to the container's interior side), so that the tube is heat-sealed whereby the liquid and the molten resin are discharged smoothly from the sealed zone to the container's interior side, when the tube is pressed together with a fluid.
In addition, Japanese Patent Laid-Open No. 53110/2000 discloses a sealing apparatus for shaping a packing material of a laminate including a synthetic resin layer into a tubular shape and for heat-sealing the tubular packing material transversely together with a fluid by using a pair of openable-and-closable pressing members including a heating mechanism, wherein a groove capable of forming a synthetic resin puddle adjacent to the outer side on the container's interior side of a sealed zone is formed on the action face of at least one of the pressing members, whereby complete sealing is achieved by guiding the liquid and dirt that have entered the very small corrugations of the inner face of the tube to flow out of the sealed zone together with the molten resin, and heat-sealing excellent in compressive strength where there is no generation of cracks due to the molten resin that had flown into the container's interior side is achieved.
Moreover, in Japanese Patent Laid-Open No. 103413/2000, it is disclosed that a high-frequency heat-sealing apparatus comprising a pair of openable-and-closable pressing members including a high-frequency heating mechanism for shaping a packing material of a laminate including a synthetic resin layer and a conductive material layer into a tubular shape and for heat-sealing the tubular packing material transversely together with a fluid, wherein a ridge shaped to contain an arcuate partial curve in its transverse contour is so formed on the action face of a high-frequency coil flush with the action face of one of the pressing members that it can press the central portion of a sealed zone having two rounded and narrowed right and left sides, and wherein a flash portion for a molten thermoplastic resin is formed adjacent to the outer side on the cutting side of the high-frequency coil, thereby achieving excellent sealing wherein no contaminants such as liquid beverages exist between the thermoplastic material layer, over the whole area of the longitudinal direction of the sealed zone, including the right and left side portions of the longitudinal direction of the sealed zone when high-frequency heated, where the width of the sealed zone is narrower compared to the width of the non-side portion.
Further, in Japanese Patent Laid-Open No. 52025/1987, it is disclosed that when an electric current flows in a high-frequency coil, a high-frequency electromagnetic field is generated around the high-frequency coil and induces an eddy current in a conductive material such as an aluminum foil, so that heat is generated in the conductive material by the eddy current to heat and melt a thermoplastic resin adjacent to the conductive material. However, the eddy current thus induced establishes round electric circuits at the two end portions of the conductive material such as an aluminum foil, so that the heated regions at the two end portions are also rounded to narrow the width of the thermoplastic material layer to be melted at the two end portions. It is also disclosed a high-frequency coil which has a linear ridge for pressing the center parts of the sealed zone, at the two narrowed right and left side portions or at the non-side portion of the sealed zone.
An Object to be Attained
In order to effect the heat-sealing properly in a high-frequency heat-sealing apparatus for transversely heat-sealing a tubular packing material filled with contents such as a liquid beverage in the presence of the liquid, it is necessary to press the thermoplastic material layers melted by the high-frequency heating, with a ridge provided on the high-frequency coil and to extrude the molten thermoplastic resin together with contaminants such as liquid beverages or the like existing between the thermoplastic material layers, from under the ridge to the two sides of the same, thereby forming a thin layer of the thermoplastic resin containing no contaminant below the ridge. It is true that achieving satisfactory heat-sealing is made possible by providing a ridge, but it did not mean that providing a ridge solved all problems. For example, there was a problem that since the face pressure of the long and narrow region being pressed by the ridge reaches approximately 100 kg/cm2, the physical strength of the press region (heat-sealed portion) becomes weak, thereby causing defective sealing, although rarely, by the damage of the press region under the ridge, when the maintenance and adjustment of the press control mechanism of the high-frequency heat-sealing apparatus is insufficient, or when the product being packed is handled in a disorderly manner. In addition, there was also a problem caused by the intensive load to the ridge portion of the high-frequency coil provided on the action face of the pressing member of a heat-sealing apparatus that was operated at high speed, wherein the work life of the pressing member was short, because of local wear-out of the ridge portion, or of the deformation of the portion that corresponds to the sealing rubber of the opposing jaw, and after activation of a relatively short period of time, replacement was needed.
On the other hand, the invention described in the aforementioned Japanese Patent Laid-Open No. 53110/2000 by the present inventors is known as a high-frequency heat-sealing apparatus that does not always need a ridge. In this heat-sealing apparatus, a groove that can form a synthetic resin puddle adjacent to the outer side on the container's interior side of a sealed zone is provided on the action face flush with the action face of a high-frequency coil, thereby making it a high quality heat-sealing apparatus capable of achieving a satisfactory sealing by guiding the liquid and dirt that have entered the very small corrugation in the inner face of the tube to flow out of the sealed zone together with the molten resin, and achieving heat-sealing excellent in compressive strength where no cracks are produced by the molten resin that has flown into the container's interior side. However, even with the use of this high-quality heat-sealing apparatus, it could not be said that the heat-sealing performance was sufficient under severe conditions with a fluid. For example, when a vegetable juice abundant in water-insoluble vegetable fiber is high-frequency heat-sealed with a fluid by using the aforementioned heat-sealing apparatus, although the cause is unknown, there were cases wherein products with defective sealing were detected at a proportion of a few to a million. An object of the present invention is to provide a very high-quality heat-sealing apparatus capable of achieving an excellent heat-sealing without providing a ridge on the action face of the high-frequency coil, wherein no defective sealing is generated even when heat-sealing under severe conditions with a fluid, such as when filling/packing a vegetable juice abundant in water-insoluble vegetable fiber.
Means to Attain the Object
In order to attain the aforementioned object, the inventors of the present invention have conducted intensive study, and manufactured many prototype heat-sealing apparatuses that do not have a ridge, effected actual heat-sealing to all of these, and observed in minute details the flow state of the molten thermoplastic resin and vegetable fiber of a sealed zone. More specifically, a sample in which vegetable juice abundant in vegetable fiber was heat-sealed with a fluid, was cut to an appropriate size, and was cut into laminae by a microtome (Japan Microtome Ltd., “RM-S model”) equipped with a diamond knife (Drukker International), in a condition wherein it was embedded in ice by using an electronic sample freezing apparatus (Japan Microtome Ltd., “EF-10 model”), and was observed and filmed by using a microscope. From the results of this study, it was discovered that when a groove inscribed in the end portion on the container's interior side of the sealed zone in which the two right and left sides are rounded and narrowed is extended over the whole area of the longitudinal direction, along the container's interior side of the sealed zone on the action face of a pressing member provided with a high-frequency coil, and a flash portion for the molten thermoplastic resin is formed adjacent to the outer side on the cutting side of the sealed zone, an excellent heat-sealing can be achieved by adopting appropriate shape, width, depth, etc, of the aforementioned groove, where there is no defective sealing even when heat-sealing under severe conditions with a fluid, such as when filling/packing vegetable juice abundant in water-insoluble vegetable fiber. It had also been discovered that a more proper heat-sealing is possible by partially changing the width of the groove and controlling the condition of the flow of the molten thermoplastic resin. The present invention had been completed based on this knowledge.
The first aspect of the present invention relates to a high-frequency heat-sealing apparatus comprising a pair of openable-and-closable pressing members including a high-frequency heating mechanism for shaping a packing material of a laminate including a thermoplastic resin layer and a conductive material layer into a tubular shape and for heat-sealing said tubular packing material transversely together with a fluid, wherein a high-frequency coil that can form a flat action face is equipped on one of the pressing members, wherein a groove inscribed in the end portion on the container's interior side of a sealed zone is formed on the action face of the pressing member which had been equipped with said high-frequency coil, and wherein a flash portion for a molten thermoplastic resin is formed adjacent to the outer side on the cutting side of the sealed zone. The second aspect of the present invention relates to the high-frequency heat-sealing apparatus according to the first aspect, wherein the other pressing member is a sealing rubber having an action face. The third aspect of the present invention relates to the high-frequency heat-sealing apparatus according to the first or second aspect, wherein the groove inscribed in the end portion on the container's interior side of the sealed zone is a groove including a partial curve, extended over the whole area of the longitudinal direction along the container's interior side of the sealed zone. The fourth aspect of the present invention relates to the heat-sealing apparatus according to any of the first to third aspects, wherein the cross section of the groove is arcuate, and the depth of the groove is no greater than one half of its width. The fifth aspect of the present invention relates to the heat-sealing apparatus according to any of the first to fourth aspects, wherein the width of the groove partially differs. The sixth aspect of the present invention relates to the high-frequency heat-sealing apparatus according to any of the first to fifth aspects, wherein a band-shaped magnetic member is provided adjacent to the outer side on the container's interior side of the high-frequency coil.